1. Field of the Invention
The invention relates to a process of manufacturing, by chemical deposit from the vapor phase, a layer of a semi-conductor composition of the elements of groups III and V onto substrates. The invention further relates to substrates which are at least partially coated with such elements.
2. Description of the Prior Art
Essentially, two types of industrial processes are presently known which make it possible to deposit a semi-conductor composition which comprises elements III and V from the vapor phase onto a substrate.
One type of process, known as the chloride process, comprises decomposing, in the presence of a substrate, a gaseous mixture constituted by a chloride of an element of group III and by an element of group V or one of its volatile compositions. The drawbacks of such a process include the necessity of requiring tightly controlled operating conditions which, specifically, necessitate several different temperature zones which must be perfectly regulated. A further drawback results because the operation of the process must take place in the presence of chlorine and/or hydrochloric acid which are themselves capable of attacking the substrate or even the deposit itself while it is in the course of being formed. Yet another problem with the process is that deposition of III-V semi-conductor compositions which are ternary or quaternary is not possible because of the strict operating conditions required.
In another known method referred to as the organo-metallic process, a gaseous mixture comprising an alkylated composition comprising a group III element and either a hydrogenated or an alkylated composition of a group V element is decomposed in the presence of a substrate. The conditions for carrying out this type of process are much more flexible than in the preceeding process and it is possible, in particular, to deposit semi-conductor compositions which are ternary or quaternary. However, to obtain the formation of a semi-conductor composition of a given stoichiometric composition having the desired electronic properties, it is necessary to use a gaseous mixture in which the concentration of the group V element is between ten and one hundred times greater than that of the group III compound and that the ratio be perfectly adjusted in this range with respect to the concentration of the group III derivative. If this condition is not closely met, the semi-conductor composition obtained is heavily doped, i.e., it has a very elevated transport number. Moreover, the process has the drawback that it leads to the necessity for an overabundant use of the group V composition. Moreover, the alkylated derivatives of group III and of group V have a very high reactivity and are, as a result, very difficult to handle and difficult to purify. Additionally, the hydrogenated derivatives of alkylated derivatives of certain group V elements (particularly arsenic and antimony) are extremely toxic and require very tight and carefully controlled operating conditions.